This invention relates to non-contacting torque sensor and an algorithm for processing signals therefrom. Currently, many of the non-contacting torque sensors employ a permanent magnet in the structure. Others utilize eddy current principles to determine the torque.
It is well known in the torque sensing art that the deformation, or twist, of a rotary shaft under load can be sensed as a measure of the torque being transmitted through the shaft. In relatively low torque applications where the amount of twist may be too small for accurate measurement, such as in automotive power steering systems, the twist is typically augmented by inserting a torsion bar between two relatively rigid sections of the shaft. The relative rotation of the more rigid sections of the shaft may be mechanically or electrically detected using a variety of techniques.
Ideally, a torque sensing arrangement should have the following characteristics. The sensor, if electrical or electromagnetic, should have a stationary transducer element, avoiding the need for slip rings or other rotating or sliding contact arrangements. This is true even in limited rotation applications, such as in automotive steering, since movement of the electrical cables increases the likelihood of failures due to mechanical fatigue or interference. The sensor should be non-contacting, meaning that the sensor elements do not physically contact each other in normal operation. Contacting operation invariably introduces hysteresis error and the possibility of failure due to mechanical bind-up. The sensor should be amenable to mass production, with liberal tolerances on the parts. The sensor should be reasonably easy to calibrate in mass production. And finally, the sensor should be capable of redundant torque measurement to permit continued operation in the event of a transducer failure.
Therefore, it would be beneficial to provide a non-contacting torque sensor that inductance variation of a coil due to the change in reluctance in a magnetic circuit when the torsion bar is under torque.